Primary cell with gelatinous electrolyte sheet



Nov. 8, 1955 J. wEsT, JR., Erm. 2,723,301

PRIMARY CELL WITH GELATINOUS ELECTROLYTE SHEET Original Filed Oct. l0,1946 gvwmvtofo JUDSON WEST JR. CHARLES E. VAN HOY United States PatentPRIMARY CELL WITH GELATINOUS ELECTROLYTE SHEET Judson West, Jr. andCharles E. Van Hoy, Fort Wayne, Ind., assignors to The Magnavox Company,Fort Wayne, Ind., a corporation of Delaware Original application October10, 1946, Serial No. 702,510. Divided and this application February 13,1951, Serial No. 210,660

3 Claims. (Cl. 136-107) This specification is a division of ourcopending application Serial No. 702,510, filed October 10, 1946, nowabandoned. p

The invention relates to improvements in dry cells, but is specificallydirected to a novel electrolytic anode for use in said cells. p

`A primary object of the invention is to provide a dry cell batterywhichmaintains uniform eiciency vsubstantially throughout its life.

Another object is to provide a cell having uniform internal resistancesubstantially throughout its life.

A further object of the invention is to provide` a cell in`which theeffective electrolyte thickness between the anode and the cathode ismaterially reduced, thus effecting a major reduction in internalresistance.

A further object of the invention is to provide a cell in which theeffective spacing between the anode and the cathode is not materiallyincreased during the life of the cellin this manner minimizing changesin internal resistance.

i A lfurther object is to provide a novel electrolyte having highconductivity and chemical activity.

.Another object is to provide an electrolyte and a cell structurewhichfhave such action that corrosion and other hazards caused byconventional free electrolytes and cell structures do not occur.` p

It is a ,further object to provide in such cells an improved method ofdepolarization which substantially prevents increase of internalresistance of the cell by preventing undesired accumulation o f gases.

A further object is to provide a cell having a relatively high*vcurrent-producing capacity in proportion' to its size and weight. n l

"Further objects and advantages willl be apparent from thedescriptionand the appended claims.

The features of the invention will be more clearly understood byreference yto the accompanying drawings and the following'descriptionthereof:

'Fig 1 is a perspective view, partly in section, showing the casing of adry cell broken away;

' Fig. 2 is a sectional view taken along line 2-2 of Fis- 1- f n Thenovel battery 11, illustrated in the drawings, cornprises at least onecell and preferably a multiplicity of cells such vas cells 12, 13, 14and 15. Each cell, for example cell 12, consists of a terminal member orcurrent collector 16, a combined cathode and depolarizer 17, a

"dialysis or ion-permeable membrane 18, a combined electrolyte-anodeform sustaining Wafer 19, and a barrier or 'current-collecting member 20of a material, such as zinc,

rthat doesnot electrochemically react with the anode material. The endterminal member 16 has an integral central boss 21 and differs in thatrespect from the correspondingcurrent collector members 22,A 23 and 24.The other end terminal 25 is identical to terminal member 16 and has anintegral boss 26. Each current collector member presents a at, generallyrectangular faceto the adjacent member or members, the` cornerspreferablyy "ice being rounded as clearly shown in Fig. 2. Themulti-cell assembly is encased in a housing or casing 27. This providesa simple construction in which each cell touches the adjacent one toprovide electrical connection in series.

Member 16 is constructed` of a material, preferably a metal such asiron, which is a good conductor and which does not electrochemicallyreact with the cathode material. The boss 21 has a bottom surfaceprojecting through an opening in casing 27 and may, if desired, lie ushwith the casing exterior surface. Boss 26 may be similarly arranged.These bosses constitute the external battery terminals. The thickness ofthe terminal members 16, 22, 23, 24 and 25 is not critical but should besucient to provide the required structural strength. As illustrative,for a cell furnishing about 1.5 volts, the thickness of each of thoseterminal members may conveniently be on the order of 0.01 inch.

' thickness of the intervening electrolyte.

In order to accomplish the several objects of this invention, amongwhich are the provision for uniform efficiency and uniform internalresistance substantially throughout the life of the device, togetherwith a relatively high current-producing capacity in proportion to thesize and weight of the cells, there is provided a novel arrangement andcoordination of cathode, anode and electrolyte. In the conventionalconstruction of dry cells, the anode and cathode of each cell are spacedapart by at least the In contradistinction thereto, pursuant to thepresent invention discrete particles of the anode material, for example,zinc, are uniformly distributed throughout the electrolyte, the

, result being that the effective electrolyte thickness is reiduced tosuch an extent that the average distance of each anode particle from thecathode is of the order of one-half of the electrolyte thickness. Thisconstruction results in increasing the conductivity of the electrolyteand in decreasing the internal resistance of the cell, since internalresistance is an inverse function of conductivity.

Another important factor in maintaining minimum internal resistance isthe novel construction of the cathode and the .method of maintainingsubstantially constant spaced relationship between the cathode and anodeparticles.

In'the present invention unitary cathode-depolarizer 17 is of wafer-likeconstruction, its thickness being relatively small in proportion to thearea presented to the electrolyte. In its particularly preferred form itis composed of selected percentages of mercuric oxide and graphite. Asthe chemical action of the electrolyte progressively reduces themercuric oxide, the effective spacing between the discrete particles ofthe anode material and the cathode is not materially increased becauseof the low ratio of cathode thickness to cathode surface area.

ForY optimum results, the cathode should be composed of an easilyreducible metallic oxide the metal of which is electronegative withrespect to the anode material, which metallic oxide is only slightlysoluble in the electrolyte. While, therefore, within the scope of thebroader aspects of this phase of the present invention, various metallicoxides may be employed as, for example,.oxi'des of copper, silver,nickel, cobalt, manganese, and iron, it has been found that mercuricoxide is exceptionally satisfactory and effective and its use in thepresent environment represents an important, but specific embodiment ofthe invention. The oxides of the other aforementioned illustrativemetals are, in general, more readily soluble than mercuric oxide in theelectrolyte and produce a lower electromotive force on open circuitsthan the cells which utilize mercuric oxide.

As previously indicated, graphite or other non-metallic conductors suchas other forms of carbon, or a mixture of graphite and other carbonforms, is mixed in selected proportions with the mercuric oxide or othermetallic oxide to form a homogeneous mixture and pressed to form awafer. in the preferred embodiment the cathode is composed of about 90to about 93 per cent mercuric oxide and about l to about 7 per centgraphite by weight. Lesser proportions of graphite tend to reduce theelectrical conductivity and render the cathode fragile, While greateramounts of graphite tend to reduce cell life for any given mass ofcathode. The homogeneous mixture of the metallic oxide and thenon-metallic conductor is placed in a forni and subjected to sucientpressure preferably without the application of external heat, to form aselfsupporting form-sustaining but porous structure. A pressure of theorder of 20,000 to 30,000 lbs. per square inch, for example, about25,000 lbs. per square inch has been found to give satisfactory resultsin most cases. The thickness of the finished wafers i7 is subject tovariation but, in general, it is preferred that the thickness be on theorder of 0.034 inch for a cell capable of producing a milliamperecurrent for sixty hours. Although it has been found that best resultsare obtained by using the above-mentioned ranges for mercurio oxide andgraphite, satisfactory results can be obtained by employing a percentageof mercuric oxide as low as 50 per cent by weight and a percentage ofgraphite as high as 50 per cent by weight. The mercurio oxide shouldpredominate in the unitary cathode-depolarizer structure.

The unitary cathode-depolarizer mixture of mercuric oxide and graphitefunctions not only as a cathode but also as a rapid depolarizer. Therapidity of depolarization or removal of accumulated gases is animportant factor in maintaining low internal resistance of a cell anduniform eiiciency substantially throughout its life. In the conventionaltype of cells in which depolarization is not accelerated, any excessivecurrent drain will cause a considerable drop in voltage, whereas cellsconstructed in accordance with the present invention on continuousdischarge at a normal rate, show no appreciable drop in Voltage untilthe full life of the battery has been reached.

In the operation of a cell embodying the present invention in itspreferred form, as the mercurio oxide in the cathode is chemicallyreduced to metallic mercury, oxygen ions migrate from the mercurio oxideto-the anode, which, when, for example, zinc is used in the anode,results in the formation of zinc oxide. Since, as previously ex*plained, discrete particles of anode material, for example, zinc, aredispersed throughout the electrolyte, such anode particles wouldnormally come into contact with the mercury resulting from the reductionof the cathode. To obviate this, an ion-permeable membrane or dialysismembrane 18 is interposed between the unitary cathode-depolarizer waferand the unitary electrolyte-anode wafer, hereinafter described, toprevent the movement of the mercury toward the anode. This membrane orconductive separator allows migration of ions.

The membrane 18 is preferably made of thin high grade parchment paper orother equivalent sheet material of a quality suitable for dialysis.While the thickness is somewhat variable, a satisfactory thickness hasbeen found to be of the order of 0.006 inch. In the construction of abattery in accordance with the present invention, the membranes arepreferably impregnated with the electrolyte before assembly in the cellsin order to render them initially conductive and to prevent loss of someof the electrolyte in Wafer 19 to the mebrane by absorption.

Unitary electrolyte-anode mixture 19 is in the form of a thin sheet orwafer of semi-solid material having high electrical conductivity andchemical activity. The electrolyte most advantageously comprises astrong alkaline or caustic solution containing a small amount of anoxide of the anode metal used, preferably zinc oxide, an anode materialin the form of discrete particles, particularly metallic zinc and agelling. agent to render the mass solid or semi-solid. The. zinc oxideassists in preventing the excessive: formation of gases which must'escape through the porous casing of the battery. To convert theelectrolyte to a solid or semi-solid state, the caustic solutioncontaining the Vadded zinc oxide is preferably intimately mixed with agelling agent and the mixture is then violently agitated while thediscrete particles of anode material, particularly amalgamated zinc, areadded. These discrete particles of Zinc, as stated, serve as the anodeof the cells of this invention. The anode must be of a readilyoxidizable metal electro positive' with respect to the cathode materialused and which will not form insoluble blocking barriers. The gelatinousmixture, in the form of sheets, is then cured, cooled and out to thedesired size of wafers. A thickness of about 0.050 to about 0.075 inchis quite satisfactory in most cases, and a thickness of 0.055 inch hasbeen found to give particularly satisfactory results. It is particularlypreferred to employ caustic soda or caustic potash las the electrolyteand, while various gelling agents may be used, carboxy methyl celluloseand salts of carboxy methyl cellulose havepbeen found to be especiallysatisfactory. Specifically, a sodium salt of carboxy methyl cellulosehas been used with excellent results, and a mixture of carboxy methylcellulose and one or more of its salts or a mixture of its salts issatisfactory. The zinc powder is advantageously amalgamated or coatedwith a thin layer of mercury prior toits addition to the electrolytegelling agent mixture. The mercury, in this case, serves to inhibitundesired local action. Y

While the proportions ofA ingredients present in the unitaryelectrolyte-anode wafers 19 are subject to variation, in general, it ispreferredvthat they fall into the following ranges, by weight: 1'7 to 20parts'ofl alkali metal hydroxide,- 50 to 70 parts of Zinc or other anodematerial, 6 to l0 parts yof gelling agent, 20 to 30 parts of water, and,where used, k2 to l parts of Zinc oxide.

The following example is illustrative of the preparation of a unitaryelectrolyte-anode Wafer suitable for use in accordance with the presentinvention. It will be understood that various changes may be made withrespect to the ingredients employed, the proportions thereof, and timesand temperature of treatment without departing from the essentialteachings and guiding principles of the present invention. Y n

75 grams of potassium hydroxide and l0 grams of zinc oxide weredissolved in milliliters of Water, and the resulting electrolyte wasthen gelled by adding l p art of carboxy methyl cellulose to 9 parts ofthe electrolyte by Weight. The mixture was then agitated at 0-l0 degreescentigrade for about ve minutes until the gelling agent was completelydispersed throughout the electrolyte. It is advantageous to operate atlow temperatures, preferably ofthe order indicated, so as to obtain asmooth homogeneous mixture having the appearance of cooked starch. Thegelled electrolyte was then vigorously stirred while addingA l part ofamalgamated zinc powder to 1 part of gelled electrolyte. Stirring wascontinued until the zinc powder was uniformly dispersed. The mixture wasthen cast into sheets of a thioknessof about 0.05 inch, cured for about1 hour at about 120 degrees centi grade, cooled for about 1/2 hour atroom temperature, and then cut into the `required dimensions to lformthe wafers for the cells. It will thus be seen that eachwafer is aself-supporting structure, easily installed, and completely eliminatesthe need for individual cell casings in multi-cell batteries.

In prior construction of multi-cell batteries it has been the practiceto maintain suchV batteries inl assembly by tapes and the like. Suchconstruction provides creeping paths or bridges for the conventionalelectrolyte and permits it to pass between cells. This action results inthe formation of high resistance'junctions between' cells, caused bycorrosion'. ln the presenti inventionthis bridging action of theelectrolyte between cells is sub'stan` tially retarded by theaforementioned novel construction of the electrolyte. To further preventany possibility. f creeping' action, barrier members 20y are providedwhich,

in their preferred form, are made of passivated Zinc or have onepassivated surface. Although it is not essential that these barriers beof the same material as the anode, they must be of a material that iselectrically conductive and which is electrochemically non-reactive withrespect to the anode and which will not introduce cell action of thewrong polarity. l

Broadly, in the embodiment of the invention barriers comprising thinsheets of Zinc are positioned between the electrolyte-anode wafer 19 andthe adjacent cell 13. Before being positioned the surfaces of thebarriers which are to be positioned adjacent the anode-electrolytewafers are subjected to a passivation treatment which makes the zincsurfaces chemically inert to the electrolyte. The functions of thepassivated barrier are to prevent the creeping of the electrolyte fromthe electrolyte-anode wafer on one side of the barrier to the adjacentcell on the other side of the barrier and to prevent undesiredelectrochemical action between said electrolyte-anode Wafer and the ironcurrent-collecting member in said adjacent cell. One suitablepassivation method consists in iirst treating the zinc with a strongcaustic solution, rinsing in distilled water and then treating thesheets in a concentrated solution of chromic oxide for about 30 seconds.The sheets are then rinsed and dried and are ready for use. Thistreatment provides a film of a chromated zinc compound of about 70microns thickness which is not readily corroded by the electrolyte whilethe shape of the barrier members prevents any appreciable movement ofthin films of the electrolyte across and over the face of these barriermembers. Specifically, as illustrated in the accompanying drawings (Fig.2), the passivated barrier takes the form of an inverted cup shape or isintegrally provided with a depending annular flange 20. This specicembodiment is more fully described and specifically claimed in anapplication Serial No. 702,809, tiled October ll, 1946, by LaVern E.Quinnell, assigned to the same assignee as the present application andinvention, entitled Dry Cell Battery.

Casing 27 serves not only completely to seal the battery structure andprevent the cells from breaking their series electrical contacts, but itis gas permeable. To achieve these results, the casing 27 is made ofmicro-crystalline wax. A thickness of the order of about 1A@ inch beingquite satisfactory in most cases. In prior cell constructions, where thecell was hermetically sealed with ordinary waxes, resins, tars, and thelike, although a rigid connection was maintained between cells the gasproduced by chemical action within the cells could not escape and theresultant pressure damaged the battery and broke the electrical contactbetween cells. By utilizing microcrystalline wax, for the casing, thisobjection is obviated.

In the present invention in the final assembly of a multi-cell batterythe individual elements and cells are placed in a stacking fixture andpressure applied to hold the parts in position while being quicklydipped in the molten micro-crystalline wax to form the casing.

It will be understood that the amount of current which can be drawn fromthe cell is dependent upon several factors, one of which is the surfacecathode area presented to the anode, while the length of time duringwhich the l Surface-Dimensions, Thickness,

Element inches Percentage by Weight of wafer 17.

While there has been shown and described what is at present consideredto be the preferred embodiment of the present invention, it will beobvious to those skilled in the art that various modifications andsubstitutions of equivalents may be made without departing from theteachings of the invention.

Having thus described our invention, we claim:

1. An electrolyte sheet for a primary cell, comprising a substantiallysolid, dimensionally stable gel consisting of water and a member of thegroup consisting of carboxymethylcellulose, salts ofcarboxymethylcellulose, and mixtures of carboxymethylcellulose and saltsof carboxymethylcellulose, and containing a caustic alkali.

2. An electrolyte sheet for a primary cell according to claim l, inwhich the alkali is sodium hydroxide.

3. An electrolyte sheet for a primary cell according to claim 1, inwhich the alkali is potassium hydroxide.

OTHER REFERENCES Industrial and Engineering Chemistry, October 1945, pp.943-944, vol. 37, No. 10.

1. AN ELECTROLYTE SHEET FOR A PRIMARY CELL, COMPRISING A SUBSTANTIALLYSOLID, DIMENSIONALLY STABLE GEL CONSISTING OF WATER AND A MEMBER OF THEGROUP CONSISTING OF CARBOXYMETHYLCELLULOSE, SALTS OFCARBOXYMETHYLCELLULOSE, AND MIXTURES OF CARBOXYMETHYLCELLULOSE AND SALTSOF CARBOXYMETHYLCELLULOSE, AND CONTAINING A CAUSTIC ALKALI.